1. Field of the Invention
This invention relates to a fine silica particles treated with a silane, and more particularly to a fine silica particles having a high dispersibility and low aggregative properties, a process for their production, and an organic resin composition containing such fine silica particles.
2. Description of the Prior Art
As methods for the surface treatment of silica with silane, commonly available methods are those in which silane is made to adhere to silica particle surfaces by treatment with silicone oil and those in which silane is chemically bonded to silica particle surfaces by treatment with hexamethydisilazane.
Properties required in organic resins, in particular, organic resin films, include transparency, blocking resistance, slip properties, scratch resistance and so forth. Adding spherical fine silica particles in organic resin films is proposed and is reported to bring about an improvement in transparency of the resultant film (Japanese Pre-examination Patent Publication (Kokai) No. 4-348147).
The silica obtained by such surface treatment can be made hydrophobic appropriately, but reactive groups such as silanol groups or alkoxyl groups remaining on the silica particle surfaces may make the silica unable to be dispersed in organic solvents of various types, or may make it highly aggregative. Accordingly, it has been sought to provide fine silica particles having a high dispersibility and low aggregative properties.
Japanese Pre-examination Patent Publication (Kokai) No. 2-160613 discloses fine silica particles having a superior dispersibility, which, however, have a problem that any heating for evaporating solvents may result in a poor primary-particle retention.
When the spherical fine silica particles disclosed in Japanese Pre-examination Patent Publication (Kokai) No. 4-348147 are compounded as a component of a heat-curable or ultra-violet-curable resin composition which is liquid in a relatively low viscosity, the fine silica particles can be dispersed with difficulty in various resins and solvents because they are inorganic matter and hence have so large a specific gravity (larger than 2.0) that they may have a great difference in specific gravity from other materials (components) of the composition, and also because the fine silica particles tend to aggregate on account of the polarity or hydrogen bond of the silanol groups they have. Thus, they have a disadvantage of sedimentation with time during the storage of the composition.
Accordingly, an object of the present invention is to provide fine silica particles having a high dispersibility and low aggregative properties, and a process for their production.
Another object of the present invention is to provide an organic resin composition which is an organic resin composition which contain fine silica particles having a high dispersibility and a high stability with time, and hence can form a film having a good transparency and superior blocking resistance, slip properties and scratch resistance.
The present invention provides silane-surface-treated fine silica particles having primary particles having a particle diameter of from 0.01 to 5 xcexcm, which fine silica particles fulfill the following conditions (i) and (ii).
(i) When an organic compound which is liquid at room temperature and has a dielectric constant of from 1 to 40 F/m and fine silica particles are mixed in a weight ratio of 5:1 and shaken, the fine silica particles disperse uniformly in the organic compound.
(ii) The quantity of primary particles remaining as primary particles when methanol is evaporated under heating by means of an evaporator from a dispersion prepared by dispersing the fine silica particles in methanol and thereafter the particles are held at a temperature of 100xc2x0 C. for 2 hours, is in a percentage of at least 20% based on the quantity of primary particles originally present.
As a process for producing the above silane-surface-treated fine silica particles, the present invention also provides a process for producing silane-surface-treated fine silica particles, comprising the steps of:
(A) introducing an R2SiO3/2 unit (wherein R2 represents a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms) to the surfaces of hydrophilic fine silica particles comprising an SiO2 unit to obtain hydrophobic fine silica particles; and
(B) introducing an R13SiO1/2 (wherein R1""s may be the same or different and each represent a substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms) to the surfaces of the resultant hydrophobic fine silica particles.
This process can provide highly dispersible and low aggregative hydrophobic fine silica particles having a particle diameter of from 0.01 to 5 xcexcm.
The present invention further provides an organic resin film comprising (a) 100 parts by weight of an organic resin and (b) from 0.01 to 10 parts by weight of the above silane-surface-treated fine silica particles.
The silane-surface-treated fine silica particles obtained by the present invention have a high dispersibility and low aggregative properties any conventional ones do not have. The present fine silica particles can preferably be used to modify properties (slip properties, wear resistance, lubricity, and anti-blocking flexibility) of various rubbers and synthetic resins, to improve properties of coating materials and ink coating agents and to impart lubricating properties and water repellency to cosmetics, and also as a fluidity-providing agent for various powders such as abrasive particles for abrasives, and powdery resins.
In particular, the organic resin composition of the present invention is formed using the above highly dispersible fine silica particles as a material, and may hardly cause the settlement of fine silica particles even with time. Hence, it can form a film having a good transparency and superior blocking resistance, slip properties and scratch resistance.
The present invention will be described below in detail.
A process for producing the fine silica particles of the present invention will be described in the order of steps.
Step (A)
In the process of the present invention, there are no particular limitations on hydrophilic fine silica particles used in the step (A) as a starting material. They may include, e.g., those obtained by a process comprising the step of subjecting a tetrafunctional silane compound represented by the general formula (I):
Si(OR3)4xe2x80x83xe2x80x83(I)
(wherein R3xe2x80x2 s may be the same or different and each represent a monovalent hydrocarbon group having 1 to 6 carbon atoms) or a partial hydrolysis-condensation product thereof or a mixture of these, to hydrolysis and condensation in a mixed solvent of water and a hydrophilic organic solvent containing a basic substance, to obtain a hydrophilic fine silica particle mixed-solvent dispersion, and subsequently the step of converting the dispersion medium of the hydrophilic fine silica particle mixed-solvent dispersion into water to prepare an aqueous hydrophilic fine silica particle dispersion.
As specific examples of the tetrafunctional silane compound represented by the general formula (I), it may include tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane and tetrabutoxysilane. As specific examples of the partial hydrolysis-condensation product of the tetrafunctional silane compound represented by the general formula (I), it may include methyl silicate and ethyl silicate. Any of these may be used alone or in combination of two or more.
There are no particular limitations on the hydrophilic organic solvent so long as it dissolves the compound of the general formula (I) or partial hydrolysis-condensation product and the water. It may include alcohols, cellosolves such as methyl cellosolve, ethyl cellosolve, butyl cellosolve and cellosolve acetate, ketones such as acetone and methyl ethyl ketone, and ethers such as dioxane and tetrahydrofuran. Preferred are alcohols. The alcohols may include alcohol solvents represented by the general formula (V):
R6OHxe2x80x83xe2x80x83(V)
(wherein R6 represents a monovalent hydrocarbon group having 1 to 6 carbon atoms). As specific examples, such alcohols may include methanol, ethanol, isopropanol and butanol. The particle diameter of fine silica particles formed increases with an increase in the number of carbon atoms of alcohols, and hence it is desirable to select the type of alcohols in accordance with the intended particle diameter of fine silica particles.
The above basic substance may include ammonia, dimethylamine and diethylamine. Any of these basic substances may be dissolved in water in a necessary quantity and thereafter the resultant aqueous solution (basic water) may be mixed with the hydrophilic organic solvent.
The water used here may preferably be in an amount of from 0.5 to 5 equivalent weight per mole of the silane compound of the general formula (I) or its partial hydrolysis-condensation product. The water and the hydrophilic organic solvent may preferably be in a ratio of from 0.5 to 10 in weight ratio. The basic substance may preferably be in an amount of from 0.01 to 1 equivalent weight per mole of the silane compound of the general formula (I) or its partial hydrolysis-condensation product.
The hydrolysis and condensation of the tetrafunctional silane compound of the general formula (I) is carried out by a known process in which the tetrafunctional silane compound of the general formula (I) is added dropwise in a mixture of the water and the hydrophilic organic solvent containing a basic substance. The dispersion medium of the hydrophilic fine silica particle mixed-solvent dispersion may be converted into water by, e.g., a process of adding water to the dispersion and evaporating the hydrophilic organic solvent (this process may optionally be repeated). The water added here may preferably be used in a 0.5-fold to 2-fold amount, and preferably about 1-fold amount, in weight ratio based on the total weight of the hydrophilic organic solvent used and alcohol formed.
The hydrophilic fine silica particles used as a starting material in the step (A) may be the mixed solvent dispersion containing hydrophilic fine silica particles, or may be an aqueous dispersion containing hydrophilic fine silica particles because the remaining alkoxyl groups are completely hydrolyzed by adding water in the hydrophilic fine silica particle mixed-solvent dispersion and evaporating the hydrophilic organic solvent to convert the dispersion medium of the dispersion into an aqueous dispersion.
Stated more specifically, the step (A) comprises, e.g., adding to an aqueous dispersion or mixed-solvent dispersion containing the hydrophilic fine silica particles a trifunctional silane compound represented by the general formula (II):
R2Si(OR4)3xe2x80x83xe2x80x83(II)
(wherein R2 represents a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, and R4xe2x80x2 s may be the same or different and each represent a monovalent hydrocarbon group having 1 to 6 carbon atoms) or a partial hydrolysis-condensation product thereof or a mixture of these, to treat the surfaces of the hydrophilic fine silica particles with it to obtain an aqueous hydrophobic fine silica particle dispersion.
As specific examples of the trifunctional silane compound represented by the general formula (II), it may include trialkoxysilanes such as methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, i-propyltrimethoxysilane, i-propyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, hexyltrimethoxysilane, trifluoropropyltrimethoxysilane and heptadecafluorodecyltrimethoxysilane. Partial hydrolysis-condensation products of these may also be used. Any of these may be used alone or in combination of two or more.
The trifunctional silane compound represented by the general formula (II) may be added in an amount of from 1 to 0.001 equivalent weight, and preferably from 0.1 to 0.01 equivalent weight, per mole of the SiO2 unit of the hydrophilic fine silica particles used.
Step (B)
Stated more specifically, the step (B) comprises, e.g., the step of converting the dispersion medium of the aqueous hydrophobic fine silica particle dispersion into a ketone solvent from the water or hydrophilic organic solvent and the alcohol mixture to obtain a hydrophobic fine silica particle ketone solvent dispersion, and the step of adding to the hydrophobic fine silica particle ketone solvent dispersion a monofunctional silazane compound represented by the general formula (III):
R13SiNHSiR13xe2x80x83xe2x80x83(III)
(wherein R1""s may be the same or different and each represent a substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms), a monofunctional silane compound represented by the general formula (IV):
R13SiXxe2x80x83xe2x80x83(IV)
(wherein R1""s are as defined in the general formula (III), and X represents a hydroxyl group or a hydrolyzable group) or a mixture of these to make triorganosilylation of reactive groups remaining on the surfaces of the hydrophobic fine silica particles.
The dispersion medium of the aqueous fine silica particle dispersion or mixed-solvent dispersion may be converted into a ketone solvent from the water or hydrophilic organic solvent and the alcohol mixture, by a process of adding a ketone solvent to the dispersion and evaporating the water or hydrophilic organic solvent and the alcohol mixture (this process may optionally be repeated). The ketone solvent added here may preferably be used in a 0.5-fold to 5-fold amount, and preferably about 1- to 2-fold amount, in weight ratio based on the weight of the hydrophilic fine silica particles used. As specific example of the ketone solvent used here, it may include methyl ethyl ketone, methyl isobutyl ketone and acetyl acetone. Preferred is methyl ethyl ketone.
As specific examples of the silazane compound represented by the general formula (III), it may include hexamethyldisilazane. As specific examples of the monofunctional silane compound represented by the general formula (IV), it may include monosilanol compounds such as trimethylsilanol and triethylsilanol, monochlorosilanes such as trimethylchlorosilane and triethylchlorosilane, monoalkoxysilanes such as trimethylmethoxysilane and trimethylethoxysilane, monoaminosilanes such as trimethylsilyldimethylamine and trimethylsilyldiethylamine and monoacyloxysilanes such as trimethylacetoxysilane. Any of these may be used alone or in combination of two or more.
These may each be used in an amount of from 0.1 to 0.5 equivalent weight, and preferably from 0.2 to 0.3 equivalent weight, per mole of the SiO2 unit of the hydrophilic fine silica particles used.
Thus, the highly dispersible and low aggregative fine silica particles having a particle diameter of from 0.01 to 5 xcexcm, and preferably from 0.01 to 1 xcexcm can be obtained in which the fine silica particles comprising SiO2 units have been coated with R2SiO3/2 units (wherein R2 is as defined in the general formula (III)) and the reactive groups remaining on the surface of these particles have been blocked with R13SiO1/2 units (wherein R1""s are as defined in the general formula (III)).
Such fine silica particles may be taken out as a powder by a conventional method, or may be obtained as a dispersion thereof to which an organic compound has been added after the reaction with silazane.
Organic Resin Composition
The organic resin composition of the present invention consists basically of (a) an organic resin and (b) the silane-surface-treated fine silica particles described above.
The componentxe2x80x94(a) organic resin used in the organic resin composition of the present invention may be either of a thermoplastic resin and a curable resin.
The thermoplastic resin may include, e.g., polyolefins such as polypropylene and polyethylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, and polyamides such as nylon 6 and nylon 66.
The composition comprising the curable resin may include, e.g., heat-curable resin compositions such as an epoxy resin composition and an unsaturated polyester resin composition, and ultraviolet-curable resin compositions such as an epoxy acrylate resin composition and a urethane acrylate resin composition.
The componentxe2x80x94(b) silane-surface-treated fine silica particles have been made highly hydrophobic, and hence are readily dispersible in various organic solvents and organic resins. Also, the silanols groups, which adversely affect the slip properties and blocking resistance of the resin film surface, are almost not present on the particle surfaces, and hence this brings about good results on the object and effect of the present invention. The present fine silica particles may preferably have a particle diameter of from 0.01 to 5 xcexcm, and more preferably from 0.05 to 1 xcexcm, in view of good slip properties and blocking resistance of the resin film surface and good transparency and also in view of the advantage that the particles may hardly settle even with time in the uncured resin composition.
Usually, the componentxe2x80x94(b) fine silica particles may preferably be compounded in an amount of from 0.01 to 10 parts by weight, and more preferably from 0.1 to 5 parts by weight, based on 100 parts by weight of the organic resin. It is easy for those who skilled in the art to determine more preferable amount within such a range in accordance with the types of resins. Its compounding in a too small amount commonly tends to make it less effective to improve the slip properties and blocking resistance of the film, and its compounding in a too large amount tends to make the resultant resin film have a low transparency and a low strength.
In addition to the components (a) and (b) described above, stabilizers such as an antioxidant and a ultraviolet light absorber, a processing aid, a colorant, an antistatic agent, a lubricant and so forth may optionally be added and compounded in the organic resin composition of the present invention so long as the effect of the present invention is not damaged
The above silane-surface-treated fine silica particles may be compounded in the organic resin by a known method, and a mixing machine such as a Henschel mixer, a V-type blender, a ribbon blender or an automatic mortar may be used. In the case when the composition has a low viscosity, the respective components in prescribed quantities may uniformly be mixed by means of a kneader mixer, a butterfly mixer or a usual mixing machine having a propeller stirrer. Thus, the organic resin composition of the present invention can be obtained.
Films may be formed from this composition by a known method, including T-die extrusion, circular die extrusion or biaxial orientation. In the case when the composition has a low viscosity, films may be formed by transferring or coating followed by hardening.
Other Uses
The silane-surface-treated fine silica particles of the present invention are also useful as an additive when polyurethane foams are produced. More specifically, the silane-surface-treated fine silica particles described above are previously added to a resin mix when polyurethane foams are produced by expanding and curing a polyurethane foam composition containing i) a resin premix containing a polyol, water as a blowing agent, a catalyst and a surface-active agent as a foam stabilizer and ii) a polyisocyanate. The silane-surface-treated fine silica particles may preferably have a particle diameter of from 0.1 to 1 xcexcm, and may usually be added in a 0.01-fold to 20-fold amount, preferably a 0.5-fold amount, in weight ratio to the polyol. The fine silica particles of the present invention do not separate or deteriorate in the resin premix, and the resin premix can stably be stored for a long term. Thus, the resin premix need not be agitated when used, and also can be free from any damage of the desired properties such as dimensional stability. In addition, it has an advantage that it can also be used in spray blowing.
The silane-surface-treated fine silica particles of the present invention are also useful as a modifying agent of printing paper. Cellulose fibers constituting a paper base may be covered with the silane-surface-treated fine silica particles of the present invention at least partly. The printing paper thus obtained can have superior printed images, water resistance and moisture resistance. Accordingly, especially when printed using printers such as ink-jet printers and laser printers, it is unnecessary to provide any flat ink-receiving layer specially as in the paper exclusively used for such printers or to use thick paper in order to improve deformation resistance at the time of high-temperature fixing. Thus, the printing paper can be used like plain paper. To obtain such paper modified with the fine silica particles of the present invention, paper may be made from a dispersion containing cellulose fibers and the fine silica particles of the present invention, or the paper base may be coated or impregnated with such a dispersion. In this instance, the fine silica particles may preferably have an average particle diameter of from 0.01 to 0.5 xcexcm.